This invention relates generally to traveling wave transport of charged particles, and more particularly to methods and apparatus for the loading, conveying and dispensing of particles as well as the monitoring and control thereof.
The following related patents and application are hereby incorporated by reference in their entirety for their teachings:
U.S. Pat. No. 4,647,179 to F. Schmidlin, issued Mar. 3, 1987, for xe2x80x9cDevelopment Apparatusxe2x80x9d;
U.S. Pat. No. 4,743,926 to F. Schmidlin, issued May 10, 1988, for xe2x80x9cDirect Electrostatic Printing Apparatus and Toner/Developer Delivery System Thereforxe2x80x9d;
U.S. Pat. No. 5,541,716, to F. Schmidlin, issued Jul. 30, 1996, for xe2x80x9cElectrostatic Toner Conditioning and Transport Systemxe2x80x9d;
U.S. Pat. No. 5,850,587 to F. Schmidlin, Issued Dec. 15, 1998, for xe2x80x9cElectrostatic Toner Conditioning and Controlling Meansxe2x80x9d; and
Co-pending U.S. application Ser. No. 09/188,458, filed Nov. 9, 1998 by F. Schmidlin, entitled xe2x80x9cXeroJetxe2x80x94A New Dry Powder Printing Processxe2x80x9d.
The present invention is related, in operation to the Dry Powder Printing Process, called XeroJet, described in co-pending application Ser. No. 09/188,458, and is based on the process of transporting dry powders using Electrostatic Traveling Waves and further includes means for confining the powder flow to narrow channels. The flow channels are preferably defined by xe2x80x9cBarrier Electrodesxe2x80x9d (BE), or xe2x80x9cguide railsxe2x80x9d, aligned parallel to the direction of flow. Barrier electrodes, in the copending application, are made extremely narrow to facilitate the formation of narrow transport channels (40 to 90 microns wide) for printing high-resolution images, including uniform solid areas. The dry powder in the XeroJet printing process is comprised of toner particles containing pigments or dyes as colorants. Independent modulation of each channel is also required to print arbitrary images.
The only essential requirement of the medium in transport, however, is that it be comprised of dry powder particles possessing an electrostatic charge (Q). This charge and the electric field (E) of the traveling wave supplies the driving force that moves the powder. As will be appreciated, aspects of the previously incorporated U.S. Pat. Nos. 5,541,716 and 5,850,587 patents are now recognized as having application to the conditioning and controlled conveyance of any chargeable dry powder. Accordingly, other powder-based applications may utilize a similar powder dispensing process, though significant benefits can ensue from application specific designs. This is illustrated herein via the design of a powder dispensing method and apparatus for use in applications pertaining to the preparation of pharmaceuticals.
Heretofore, a number of patents and publications have disclosed traveling wave transport for the transport of charged toner particles, the relevant portions of which may be briefly summarized as follows:
U.S. Pat. No. 4,647,179, issued Mar. 3, 1987, teaches a traveling wave transport for conveying toner from a supply to a development station where the toner is used to form images. FIGS. 3-5 illustrate electrode arrays for accomplishing the traveling wave transport apparatus.
U.S. Pat. No. 4,743,926, issued May 10, 1988, discloses a developer or toner delivery system for presenting toner to a charged surface or addressable printhead. Moreover, FIG. 4 therein depicts a toner charging apparatus including a corona charging means (corona wire) and a toner separator for transporting oppositely charged toner particles, one to a print medium and the other being returned to a toner sump.
Fred Schmidlin, xe2x80x9cA New Nonlevitated Mode of Traveling Wave Toner Transportxe2x80x9d, IEEE Transactions on Industry Applications, Vol. 27, No. 3, May/June 1991), where toner particles were disclosed as moving in an aerosol state as tiny linear clouds, with one such cloud confined in the potential trough of each wave.
As evidenced by U.S. Pat. Nos. 5,846,595 and 5,858,099 to Sun et al., hereby incorporated by reference for their teachings, pharmaceutical manufacturers utilize a xerographic like development process to deposit charged pharmaceutical powders on an electrostatic receiver electrode comprised of separated voltage patches. The powder mass per patch is controlled in part by: the area of a patch, the voltage on the receiver electrode and the average charge/mass of the powder particles.
Recognizing the ability to move a large quantity of charged particles with a high degree of control, the present invention seeks to combine novel aspects and improvements of traveling wave transport to provide an efficient and highly accurate method and apparatus for the loading, conveying and dispensing of pharmaceutical compounds (particles) as well as the monitoring and control thereof.
In accordance with the present invention, there is provided an apparatus for conveying electrostatically charged particles to a particle receiver, including: a traveling electrostatic wave conveyor for conveying the electrostatically charged particles from a source at a first end thereof to a receiver at a second end thereof; and barrier electrodes overlaid on said conveyor from the first end to the second end, said electrodes dividing said conveyor into parallel columns and forming isolated potential wells to receive packets of particles therein and to convey said packets to said receiver, wherein the barrier electrodes are connected to a common bus.
In accordance with another aspect of the present invention, there is provided An apparatus for conveying electrostatically charged particles to a particle receiver and estimating the mass of electrostatically charged particles conveyed thereon, including: a traveling electrostatic wave conveyor for conveying the electrostatically charged particles along a surface thereof from a source of particles to a particle receiver; barrier electrodes overlaid on said conveyor in the direction of travel from the particle source to the receiver, said electrodes dividing said conveyor into parallel columns and forming isolated potential wells to receive packets of particles therein and to convey said packets to said receiver, wherein the barrier electrodes are connected to a common bus; and a photodetector directed to receive light reflected from the electrostatically charged particles, wherein the output signal of said photodetector is proportional to the mass density of the particles being conveyed.
In accordance with yet another aspect of the present invention, there is provided a method for extracting charged particles from a fluidized bed of particles and loading the particles on to a traveling wave conveyor, comprising: electrically isolating at least one segment of the traveling wave conveyor; operating the at least one segment of the traveling wave conveyor at a voltage slightly above a corona generating voltage; and immersing the at least one segment within the fluidized bed, where the at least one segment operating above the corona threshold voltage will charge the particles and advance the charged particles to an adjoining segment of the traveling wave conveyor, the segments of which are operated at a voltage below the corona generating voltage.
One aspect of the invention is based on the discovery of techniques for the use and modifications of the electrostatic transport and control means described relative to printing equipment to produce a powder dispensing method and apparatus suitable for the manufacture of oral pharmaceuticals (e.g. tablets, pills, capsules). More specifically, one aspect of the present invention deals with a basic problem in the preparation of pharmaceuticalsxe2x80x94the accurate measurement of various components on a mass production scale. Hence, the present invention is directed to a means of dispensing accurately controlled, isolated quantities of powder or particles in the sub-milligram to several milligram mass range.
The techniques described herein are advantageous because they provide a simple, yet highly accurate means for transporting pharmaceutical components or other dry-powder compounds from a source to a receiver. The technique is further suited for automated high volume production and packaging of pharmaceuticals at low cost. Such methods and apparatus make it unnecessary to have expensive weighing equipment. Moreover, the system is flexible enough so as to be applicable to a number of different powder or particulate dispensing situations, and is not limited to pharmaceuticals.